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Proper prop selection and other things like wings but not exactly the same...


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#1 Plank

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Posted 21 February 2018 - 20:07

Hello!

 

Well I am still learning! Yey! Even at my age... ( late 40's )

 

So we have two major dimensions for propellers ( fixed pitch ! )

 

The width. ( Diameter of the swept circle ...)

 

The one revolution distance traveled forward or "pitch"

 

So a 8 x 4 propeller is 8" in diameter and has a full rotation pitch of 4".

 

( To clear up any issues with pitch: the propeller is an "air screw" and does exactly that.

So the the distance it travels in one rotation is the "pitch". If we were to look a stationary

propeller and then rotate it one turn it would move a linear column of air n inches... and this

would be it's pitch.)

 

So what do the numbers really mean?

 

Small diameter is less swept air, larger diameter is more swept air.

Small diameter at n rev's is less power use, large diameter at n rev's is more power use.

Small diameter will air brake less, large diameter will air brake more.

Less pitch is less air column shifted , more pitch is more air column shifted.

Less pitch is more linear torque/less rotational torque, more pitch is ~ versa.

Less pitch is more air braking at higher speed, more pitch is less air braking at high speed.

 

 

So a small diameter and low pitch prop will:

 

sweep not much air, use less power, air brakes less, shift less air column, more LT, less RT, more air braking. ( With respect to above table.)

 

and smaller props weigh less. obviously.

 

Props for climbing/prop hanging and props for high speed.

 

lets say we use an 11" prop in 4" inch pitch and in 8" pitch.

 

Ignoring all but the basics you will find the 4" prop will yank your plane along to a point then it won't go any faster, conversely the 8" will slowly fly up to a much higher top speed.

 

Want to have oodles of pull? Go for a lower pitch.

 

Want to fly fast? go for higher pitch.

 

Why is this important?

 

Well if you are flying your N28 at low speed and feel that it's just a gutless piece of crap...

maybe you have the wrong prop on....

 

( Imagine if you had the right one on... lower top speed BUT oodles of pull...)

 

Will prop specs get modeled in FC... causally wondering... he said reaching for the second Gin and tonic for the morning.... oh look the sun is out...

 

 

Props: the other other fixed wing...

 

Salute!

 

Planky.


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#2 US103_Baer

US103_Baer
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Posted 22 February 2018 - 04:51

With you on this Plank, not that I expect to see it at this point, but future Sims will.

Look at car racing Sims. Nearly everything historically adjustable is adjustable in game. Anything less wouldn't be accepted by users. Ride height, toe in/out, camber, spring rates, bump stops, diff ratios etc.

There must be quite a few changes that were fairly standard adjustments a pilot would make to customize his aircraft.

Apart from propellor selection, one thinks of rigging, tailplane incidence, engine/prop gearing, high compression pistons (ace squadrons), and even dihedral. The latter apparently a well documented mod by Bill Lambert with his SE5a.

Appropriate to plane type of course
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#3 J2_Trupobaw

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Posted 22 February 2018 - 07:36

1. During WW1, there were different fixed-pitch props fixed to the same plane. Much of historical data inconsistency (different speeds and climb speeds recorded for same machine) is said to come from different props used. Or so I heard.

2. FC will import RoF content as it is, so we shouldn't expect new props out of the box. However...

3. BoX engine already supports different prop pitches, and BoX plane mods can go as far as engine swaps. So having a different prop as a field mod will be possible (and shouldn't be hard...).


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#4 J2_PikeStance

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Posted 22 February 2018 - 08:14

You know when I first got into RoF, I actually thought Modification referred to actual modification of the plane. I had no idea it was just instrumented (some have guns, etc..). I really thought it was stuff like changes pilot and crewman made to plane during the war. 


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#5 Plank

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Posted 22 February 2018 - 19:46

Imagine tweaking your MG's to fire up a bit more and then sighting in your sights to whatever distance you like...

All at the gunnery range provided in the box.

 

Cough:

 

Jack up the tail till your plane is "level" ( whatever level is in RoF...)

Set up the target distance. Say 200m. ( a big targety type thing )

Set up target position. ( up/dn Lefty/righty. )

Shoot off some rounds.

Fiddle with MG mounts till your rounds hit the target. ( !!! )

Fiddle with sights to seal the deal.

 

Comes with a borescope!

 

Viola! guns now set to 200m at whatever inclination you desire. or not.

 

( it is possible that straffers might want their guns pointing down a tad... )

 

 

chuck on the long short pitch prop and go get some in the furball!

Look a prop hanging N28!!!! all 160hp of glorious motor going flat knacker!

 

" Yes it's dynamite up to 102.7 Mph then it tends to drink petrol like a maniac and not go any faster, but it never slows down no matter what you do with it. Jolly good fun. and the propwash is pure insanity. on a cold damp day you can almost land it vertically..." He said while loading another gin bottle into the pannier of his bicycle.

 

"Get a good selection of props and try them all out. I am pretty sure you will find the one you want. Even."

And with that he saluted and rode off back to the AF, clinking gently as he went.

 

Salute!

 

Planky.


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#6 Chill31

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Posted 22 February 2018 - 20:06

So changing the pitch on 160 Gnome would be an interesting thing since it has no throttle.

You would be limited by upper rev limit because you could not throttle back to protect the engine, the is only the ignition sequencer
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#7 Plank

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Posted 23 February 2018 - 01:49

Hello!

 

I guess you can keep the load on the engine the same with different pitch blades by varying the diameter.

 

Q: Is the plane while chocked on the ground presenting the most load to the engine ?

( If this is so then you should be able to  cycle through a selection of props to find one that suits ...)

 

and I suppose starting a gnome without a prop is a really bad idea....

 

and all the planes which used the gnome must have had different props...

 

Salute!

 

Plank.


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#8 Chill31

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Posted 23 February 2018 - 12:41

That's true. Your diameter though would be limited by propeller-ground clearance during take off and landing.

On the ground, at full power is the highest load on the engine.

That in mind, a max climb prop for a given engine would be essentially the same regardless of the aircraft. You would have to balance climb with top speed. On the 160 Gnome, the ignition selector has specific firing sequences (I don't remember them right off) to reduce engine speed.

This would be a cool idea to do a custom pitch propeller. I have no idea how practical it is to implement since the prop curves are not simply pitch-diameter based. I will see if I can find the charts I used for FSX, which is the same way they do it in ROF.
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#9 Arty_Effem

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Posted 24 February 2018 - 10:13

On the ground, at full power is the highest load on the engine.
 

 

It's a shame that most of the engines in RoF aren't aware of that basic fact, mysteriously providing more RPM at zero airspeed, which then reduces during initial acceleration.

It's obviously a fudge to disguise an inconsistency in the flight model, but it's likely it would make a mockery of the exercise under discussion.

 

 

On the 160 Gnome, the ignition selector has specific firing sequences (I don't remember them right off) to reduce engine speed.7

 

I believe the intermediate sequences are:

 

Fire every second cylinder

 "        "      fourth   "        "

 "        "      eighth   "        "


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